The present invention relates to an improvement in electric vehicles driven by electric motors, and more particularly, relates to control in switching an electric vehicle in forward travel to reverse travel.
An electric vehicle of this kind is disclosed, for example, in Japanese Patent Laid-Open Publication No. HEI-3-98404 entitled xe2x80x9cCompact Electric Vehicle.xe2x80x9d This electric vehicle includes an electric motor as a driving source, a drive circuit for the electric motor, an electromagnetic brake which releases the brake when being energized, a controller for controlling the electric motor and the electromagnetic brake, an acceleration setting volume, and a switch for switching between forward and reverse travel which allows a choice between forward or reverse travel and selection from among low, middle and high speeds.
In order to switch the direction of the electric vehicle from forward travel to reverse travel by the switch, the acceleration setting volume is returned to zero (zero motor rotation) before forward/reverse switching of the switch.
For some reason, however, the switch can be switched from forward travel to reverse travel without returning the acceleration setting volume to zero. This requires reversing the polarity of a motor drive circuit, resulting in a heavy load applied to switching elements constituting the motor drive circuit. It is thus necessary to use large-capacity switching elements endurable to the load.
Large-capacity switching elements inevitably cost high and have large size. This undesirably boosts the cost of the vehicle. An electric vehicle which allows reduction in load applied to a motor control circuit is thus desired.
According to the present invention, there is provided an electric vehicle driven by electric motors, which comprises: a directional speed member for instructing forward travel, neutral and reverse travel of the vehicle and adjusting the speed of the vehicle; the electric motors which operate in accordance with the operation of the directional speed member; and a controller for performing such control as, when two conditions are satisfied that time required for the directional speed member to pass through a neutral region is shorter than a threshold and the electric motors are still rotating in a forward direction at a point of time when the directional speed member is shifted from the neutral region to a reverse region, waiting until the speed of the electric motors becomes zero, and, after a lapse of time required for forward/reverse switching of the motor drive circuits since the speed of the electric motors reaches zero, shifting to normal reverse operation.
This invention thus first determines whether the directional speed member is switched at a xe2x80x9cnormalxe2x80x9d speed or a xe2x80x9chigh speed.xe2x80x9d When the xe2x80x9chigh speedxe2x80x9d switching is found, this invention waits until the speed of the electric motors becomes zero. This invention further waits until time required for forward/reverse switching of the motor circuits has elapsed and then performs reverse control. This allows reduction in electrical load applied to the motor circuits, allowing reduction in capacity of switching elements and reduction in cost of the circuits.
However, when the traveling speed of the vehicle is low, since switching of the directional speed member from forward travel to reverse travel at a high speed does not apply a large load to the motor drive circuits, the vehicle is operated during a period of time required for forward/reverse switching of the motor drive circuits, resulting in smoothness of the operation.